Much research in science education has focused on the processes of knowledge building and comprehension of scientific content. However, the positive roles of what is unknown or not understood have received much less attention. This article is the second one of two reviews that analyze the nature of what is consciously unknown or not understood about science content. The first paper focused on the components and structure of incomprehension. This second paper examines the variables influencing what is consciously not known or not understood. In particular we review and synthesize studies about the influence of knowledge, tasks, and standards of coherence on the awareness of lack of knowledge or the incomprehension of science, that is made explicit through questioning. Finally, we synthesize some implications of the revised studies for science teaching and learning.